Web advertisers perform targeting with the aim of presenting users who have accessed their webpages with information such as targeted advertisements which are suited to interests and choices of the users. The Web advertisers track a user by using an ID called an HTTP cookie issued to a browser, and creates a profile related to data on interests and choices of the user.
Recently, there has been a demand for more data on interests and choices of a user to be collected in order to present more appropriate information to the user. It is, however, not easy to know whether or not a user whose data on interests and choices are collected on a certain webpage and a user whose data on interests and choices are collected on another webpage are identical.
In light of this, for example, Patent Literature (PTL) 1 proposes a technique of collecting records of actions taken by a user on a first medium and associating identical users on the basis of user identification information specified upon logging in to a second medium.